I don't think this pessimism and defeatism belongs to the public at large. There is an anxiety present there, to be sure, and the corrupt media have translated that into pessimism to advance their left-wing masters into power.
That pessimism isn't based on reason, so it probably won't respond to reason. No amount of heads -- including that of Osama bin Laden himself -- is going to sway the liberal propaganda machine from its intended purpose: the betrayal of America.
We MUST NOT win this war!
Oh.
One might recall that in 1968, the Wise Men, a group of Democratic policymakers that included Dean Acheson, Clark Clifford, and Mac Bundy and which shaped our Cold War policy under Truman, lost their nerve over the Vietnam War, into which they had done so much to get the US involved. In March of that year, right after our troops had won a major victory in turning back the North Vietnamese Winter-Spring Offensive, and with the public still supporting the war effort, these Wise Men told President Johnson that the war could not be won.